Preparation of Tritium

Because tritium occurs in nature only as an extreme trace, it must be manufactured artificially rather than isolated from a natural source. The standard method bombards lithium-6 with slow (thermal) neutrons inside a nuclear (fission) reactor, in a nuclear transmutation reaction that also produces helium-4:

$_3^6Li + \,_0^1n \rightarrow \,_2^4He + \,_1^3T$ …